Hi Marek,
Thanks for reaching out to Microsoft Q&A.
Please check if you can restore the account as per below steps:
When you delete a user account for a customer, the account is set to the status of Inactive for 30 days. During this time, you can restore the account.
Appropriate GDAP roles: Directory Writer | User Admin
To restore a deleted user account, use the following steps:
- Sign in to Partner Center and select Customers.
- Select the customers to be restored from the Customer list.
- In the customer menu, select Users and licenses.
- Restore the user:
- Pilot users: Select Restore from the top of the page, then select the user to restore, then select Restore. (If there are no users that can be restored, the Restore option is greyed out.)
- All other users: Select Users and licenses, then select Deleted users (#), where # is the number of users you've selected to restore.
If above steps are not helpful, then please create a support ticket here - https://partner.microsoft.com/en-us/support?stage=3&topicid=6b52f3cf-3b36-df07-f75b-27aa68bf8a01
Reference Link: https://learn.microsoft.com/en-us/partner-center/account-settings/unable-to-sign-in
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